Optical element inspection device and optical element inspection method

ABSTRACT

To provide an optical element inspection device and an optical element inspection method capable of inspecting the relative position of each reflective surface of an optical element. An optical element inspection device comprises a pedestal  610  with a cross-dichroic prism  45  installed thereon, an autocollimator  620  which introduces the measurement light into any of four reflective surfaces at the angle of incidence of  45 °, and detects the return light thereof, and a switching device  630  for introducing the measurement light into only either a left area or a right area. The relative position between two reflective surfaces of each color reflective surface can be easily inspected by introducing the measurement light in only the reflective surface of either area of the color reflective surface by a switching device  630.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates to an optical element inspectiondevice and an optical element inspection method.

[0003] 2. Description of Related Art

[0004] A projector comprising a plurality of liquid crystal panelscapable of modulating a plurality of color lights for each color lightaccording to image information, a cross-dichroic prism for an opticalelement for synthesizing the color lights modulated by each liquidcrystal panel, and a projection lens for forming a projected image byprojecting the light beam synthesized by this cross-dichroic prism in anenlarging manner has been in use. Such a projector separates, forexample, the light beam emitted from a light source into three colorlights of RGB by a dichroic mirror, performs modulation according toimage information for each color light by three liquid crystal panels,synthesizes the modulated light beam by a cross-dichroic prism, andprojects a color image in an enlarging manner via the projection lens.

[0005] Such a cross-dichroic prism is a substantially cubic prism formedby affixing four rectangular prisms along each interface. In addition, adielectric multi-layer film for reflecting red light having apredetermined wavelength range is provided in a set of two reflectivesurfaces along the extending direction at four affixing surfaces, and adielectric multi-layer film for reflecting blue light having awavelength range different from the above is provided in a set of theother two reflective surfaces along the extending direction. This meansthat four reflective surfaces are disposed in an X-shape inside thecross-dichroic prism.

[0006] Thus, in order to obtain a sharp projected image, each X-shapedreflective surface must reliably face the predetermined direction withrespect to each liquid crystal panel. Therefore, in a conventionalpractice, the cross-dichroic prism is fixed to a fixing member with highaccuracy for unification based on the intersection formed by butting thecontour dimension of the cross-dichroic prism against an end of eachrectangular prism, i.e., the intersection of the reflective surface forreflecting red light with the reflective surface for reflecting bluelight, and, accommodated in the projector together with this unit tospecify the direction of each reflective surface.

SUMMARY OF THE INVENTION

[0007] However, in such a method, the cross-dichroic prism is onlyadjusted by the contour standard though the position of thecross-dichroic prism with respect to each liquid crystal panel can beadjusted, and a problem occurs, in that any relative positionaldeviation between each reflective surface inside the cross-dichroicprism cannot be inspected.

[0008] Such a problem occurs not only in the above cross-dichroic prism,but also in other optical elements such as affixed mirrors having forreflective surfaces.

[0009] An object of the present invention is to provide an opticalelement inspection device and an optical element inspection methodcapable of inspecting the relative position of each reflective surfacein an optical element.

[0010] [Means for Solving the Problems]

[0011] The optical element inspection device of the present invention ischaracterized in that it inspects the relative position of eachreflective surface of the optical element having four reflectivesurfaces disposed in X-shape so as to form the angle of incidence of 45°when viewed in the direction orthogonal to the optical axis of theincident light beam so that one set of reflective surfaces along oneX-shaped extending direction reflect the light beam of the wavelengthrange different from that of the other set of reflective surface, andcomprises a pedestal on which the optical element to be inspected isinstalled, a measurement light introduction unit for introducing themeasurement light at the angle of incidence of 45° with respect toeither of the above four reflective surfaces, a return light detectionunit for detecting the return light of the measurement light introducedin the above optical element from this measurement light introductionunit, and a measurement light switching unit for introducing themeasurement light only in either area of two areas demarcated by theintersection of one set of the reflective surfaces with the other set ofreflective surfaces when viewed in the introducing direction of themeasurement light.

[0012] In the present invention, the inspection is carried out, forexample, in the following procedure.

[0013] Firstly, the optical element to be inspected is installed on thepedestal, and the measurement light is introduced only in either area oftwo areas demarcated by the intersection at the angle of incidence of45° from the measurement light introduction unit. Then, the return lightof the measurement light introduced in the reflective surface of onearea from this measurement light introduction unit is detected by areturn light detection unit. Next, the measurement light is introducedonly in the other area of the two areas demarcated by the intersectionby a measurement light switching unit, and similarly to the above, thereturn light of the measurement light introduced in the reflectivesurface of the other area from the measurement light introduction unitis detected by the return light detection unit.

[0014] Then, the relative position between the two reflective surfacesin one set is inspected by comparing the results of detection of thereturn light from each reflective surface with each other in one set ofthe reflective surfaces along the extending direction, and acquiring thedeviation thereof. Similarly, in the other set of reflective surfacesalong the extending direction, the deviation is acquired, and therelative position between the other set of two reflective surfaces isalso inspected.

[0015] In such an inspection system, the relative position between thetwo reflective surfaces in each set can be inspected easily. Thus, theacceptance or rejection determination accuracy of the optical elementcan be improved. Further, the projected image of the projector can besharp by building the optical element determined to be acceptable insuch an inspection in the projector or the like.

[0016] In such an optical element inspection device, the measurementlight introduction unit and the return light detection unit arepreferably integrated with each other for an autocollimator.

[0017] In such a configuration, the measurement light introduction unitand the return light detection unit form one appliance for theintegrated autocollimator, and the optical element inspection device canbe miniaturized in comparison with a case in which measurement lightintroduction unit and the return light detection unit are disposedseparately from each other.

[0018] The optical element inspection device preferably comprises areflecting member which reflects the light beam reflected by thereflective surface and introduces it in the return light detection unitas the return light.

[0019] In this configuration, the light beam reliably reflected by thereflecting member forms the return light, and in comparison with a casein which the light beam reflected by, for example, an end face of aprism forms the return light, the return light can be brighter, andeasily detected by the return light detection unit.

[0020] In addition, the return light detection unit preferably includesa color separation optical system for separating the return light into aplurality of color lights, and a plurality of image pickup elementsaccording to each color light separated by this color separation opticalsystem.

[0021] A CCD (Charge Coupled Device) etc. can be employed for the imagepickup element.

[0022] In such a configuration, the return light including light beamsof different wavelength ranges is automatically detected substantiallyat the same time by separating the return light into each color light bythe color separation optical system, and picking up the image for eachseparated color light by each image pickup element.

[0023] Since the return light is thus detected, the return light can bemore reliably and automatically detected than the configuration in whichthe return light is visually detected, and the burden on operators canbe reduced.

[0024] There is another configuration in which a plurality of colorfilters consisting of each color (of the predetermined wavelength range)are prepared in place of the above configuration, the return light fromthe optical element is successively passed through these color filters,and the return light is detected by the return light detection unit foreach color light. However, the return light can be more easily detectedin the configuration in which the color separation optical system andthe image pickup element are employed as described above since the colorfilter need not be replaced.

[0025] The optical element inspection device including the colorseparation optical system and the image pickup element preferablycomprises an image take-in unit for taking in the signal detected by theimage pickup element, and a reflective surface angle differencemeasurement unit which performs the image processing of the image signaltaken in by this image take-in unit, and measures the angle formed bythe one set of reflective surfaces or the other set of reflectivesurfaces.

[0026] In this configuration, the return light is detected by the imagepickup element, the detected signal is taken in by the image take-inunit, and the image of this taken-in image signal is processed by theimage processing unit.

[0027] Then, the angle formed between two reflective surfaces in eachset is measured by the reflective surface angle difference measurementunit based on the position of each image-processed return light at tworeflective surfaces in each set, and the angular deviation between thetwo reflective surfaces in each set can be easily and automaticallyinspected only by setting the acceptable angular range in advance.

[0028] The above optical element inspection device preferably comprisesan intersection image pickup unit for picking up an image of theintersection of the reflective surfaces of the one set with thereflective surfaces of the other set, and a joining conditiondetermination unit for determining the joining condition of eachreflective surface from the width and the inclination of theintersection based on the signal detected by this intersection imagepickup unit.

[0029] Here, the joining condition of each reflective surface means acondition of the relative position between the reflective surfacesincluding how much two reflective surfaces are deviated in translationin the direction orthogonal to the extending direction, and how much tworeflective surfaces are inclined from the direction normal to theoptical axis.

[0030] As described above, the width of the intersection is measured bythe intersection image pickup unit, and even when the two reflectivesurfaces in each set are deviated in translation, the deviation for thistranslation can be easily inspected. In addition, the inclination of theintersection is measured by the intersection image pickup unit, thedeviation of this inclination can be easily inspected even when the tworeflective surfaces in each set are deviated in inclination from thereference axis normal to the optical axis of the incident light beam.Automatic inspection can be easily carried out only by presetting theacceptable range of the width and the inclination.

[0031] The optical element inspection method of the present invention isan optical element inspection method for inspecting the relativeposition of each reflective surface of an optical element having fourreflective surfaces disposed in X-shape so as to form the angle ofincidence of 45° when viewed in the direction orthogonal to the opticalaxis of the incident light beam with one set of reflective surfacesalong one extending direction of a letter X reflecting the light beam ofthe wavelength range different from that of the other set of reflectivesurfaces, and comprises a measurement light introducing procedure ofintroducing the measurement light at the angle of incidence of 45° ineither reflective surface of the optical element to be inspected, areturn light detecting procedure of detecting the return light of themeasurement light introduced in the optical element by this measurementlight introducing procedure, a measurement light switching procedure ofswitching the measurement light into another reflective surface alongeither reflective surface, and introducing it, and a deviation detectingprocedure of detecting the return light of the switched measurementlight, and detecting the deviation of the other reflective surface withrespect to either reflective surface.

[0032] In the present invention, the inspection is carried out in thefollowing procedures described below.

[0033] Firstly, the optical element to be inspected is installed, andthe measurement light is introduced only in either reflective surface atthe angle of incidence of 45° by the measurement light introducingprocedure. Then, the return light of the measurement light introduced ineither reflective surface is detected by the return light detectingprocedure.

[0034] Next, the measurement light is introduced only in the otherreflective surface along the either reflective surface by themeasurement light switching procedure. After than, the deviation of theother reflective surface with respect to either reflective surface isdetected based on the result of detection of the switched measurementlight and the result of detection by the return light detecting means bythe deviation detecting procedure.

[0035] In this inspection, the relative position between two reflectivesurfaces along the extending direction can be easily inspected, andacceptance or rejection of the optical element can be determined withhigh accuracy. In addition, the projected image of the projector can besharpened by building the optical element determined to be acceptable bythe inspection in the projector or the like.

[0036] The above optical element inspection method preferably comprisesan intersection image acquiring procedure of acquiring an image of theintersection of the one set of reflective surfaces with the other set ofreflective surfaces, and a joining condition determining procedure ofdetermining the joining condition of each reflective surface from thewidth and the inclination of the intersection.

[0037] In this configuration, automatic inspection can be easily carriedout only by installing the acceptable range of the width and theinclination in advance, acquiring the intersection image of thereflective surfaces by the intersection image acquiring procedure, anddetermining whether or not the width and the inclination of the acquiredintersection image are within the acceptable range by the joiningcondition determining procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a schematic diagram showing a structure of a projectorincluding a cross-dichroic prism as an optical element to be inspectedby an optical element inspection device according to an embodiment ofthe present invention.

[0039]FIG. 2 is an overall perspective view showing a structure of theprojector.

[0040]FIG. 3 is an exploded plan view showing the cross-dichroic prism.

[0041]FIG. 4 is a perspective view showing a structure of an opticalparts in the above embodiment.

[0042]FIG. 5 is a plan view showing a fixed plate in the aboveembodiment.

[0043]FIG. 6 is a side view showing the cross-dichroic prism and thefixed plate in the above embodiment.

[0044]FIG. 7 is a front view showing the optical element inspectiondevice.

[0045]FIG. 8 is a plan view showing the optical element inspectiondevice.

[0046]FIG. 9 is a side view showing the optical element inspectiondevice.

[0047]FIG. 10 is a view showing an autocollimator in the aboveembodiment.

[0048]FIG. 11 is a view showing a major part of a 3CCD camera in theautocollimator.

[0049]FIG. 12 is a block diagram showing a processing unit in theembodiment.

[0050]FIG. 13 is a front view showing switching device the opticalelement inspection device.

[0051]FIG. 14 is a side view showing the switching device.

[0052]FIG. 15 is a block diagram showing a computer in the embodiment.

[0053]FIG. 16 is a flowchart showing an inspection procedure by theinspection device.

[0054]FIG. 17 is a flowchart describing a procedure for adjusting theautocollimator of the embodiment.

[0055]FIG. 18 is a flowchart describing a procedure for adjusting areflecting mirror in the embodiment.

[0056]FIG. 19 is a flowchart describing a procedure for adjusting a CCDcamera in the embodiment.

[0057]FIG. 20 is a view for describing a procedure for adjusting a CCDcamera in the embodiment.

[0058]FIG. 21 is a flowchart for describing a procedure for inspectingthe deviation of each reflective surface in the embodiment.

[0059]FIG. 22 is a view showing the return light on a display in theembodiment.

[0060]FIG. 23 is a view showing the deviation of the reflective surfacein the cross-dichroic prism.

[0061]FIG. 24 is a view showing the deviation of the reflective surfacein the cross-dichroic prism.

[0062]FIG. 25 is a flowchart describing a procedure for inspecting therelative position of each reflective surface in the embodiment.

[0063]FIG. 26 is a view showing the return light of each reflectivesurface on the display in the embodiment.

[0064]FIG. 27 is a view showing the deviation between reflectivesurfaces in the cross-dichroic prism.

[0065]FIG. 28 is a flowchart for inspecting the joining condition of thereflective surfaces of the cross-dichroic prism.

[0066]FIG. 29 is a view showing the joining condition of the reflectivesurfaces of the cross-dichroic prism.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0067] An embodiment of the present invention will be described withreference to the drawings.

[0068] [1. Structure of Projector]

[0069]FIGS. 1 and 2 show a projector 1 having a cross-dichroic prism 45for an optical element to be inspected.

[0070] The projector 1 comprises a power source unit 3 accommodated inan external case and an optical unit 4 of U-shape in plan view similarlydisposed in the external case, and is substantially rectangularparallelopiped on the whole as shown in FIGS. 1 and 2.

[0071] The power source unit 3 comprises a power source 31 and a lampdrive circuit (ballast) 32 disposed on the side of the power source 31.

[0072] The power source 31 supplies the power supplied through a powersupply cable to the lamp drive circuit 32 and a driver board, etc. (notshown), and has an inlet connector 33 in which the power supply cable isinserted. The lamp drive circuit 32 supplies the power to a light sourcelamp 411 of the optical unit 4.

[0073] The optical unit 4 forms an optical image corresponding to imageinformation by optically processing the light beam emitted from thelight source lamp 411, and comprises an integrator illumination opticalsystem 41, a color separation optical system 42, a relay optical system43, an electro-optical device 44, a cross-dichroic prism 45 for anoptical element, and a projection lens 46.

[0074] [2. Configuration of Optical System]

[0075] The integrator illumination optical system 41 illuminates animage forming area of three liquid crystal panels 441 (referred to asliquid crystal panels 441R, 441G and 441B, respectively for each colorof red, green and blue) constituting the electro-optical device 44 in asubstantially uniform manner, and comprises a light source device 413, afirst lens array 418, a second lens array 414 including a UV filter, apolarization conversion element 415, a first condenser lens 416, areflecting mirror 424, and a second condenser lens 419.

[0076] The light source device 413 comprises a light source lamp 411 fora radial light source for emitting radial light, and a reflector 412 forreflecting the emitted light from the light source lamp 411. The lightsource lamp 411 often includes a halogen lamp and a metal halide lamp,or a high voltage mercury lamp. A parabolic mirror is used for thereflector 412. An elliptic mirror together with a parallel lens (concavelens) may be used in addition to the parabolic mirror.

[0077] The first lens array 418 has a configuration in which small lenshaving substantially rectangular contour are arrayed in a matrix whenviewed from the direction of the optical axis. Each small lens splitsthe light beam emitted from the light source lamp 411 into a pluralityof sub light beams. The shape of the contour of each small lens is setso as to be substantially similar to the shape of the image forming areaof the liquid crystal panel 441. For example, if the aspect ratio (theratio of the transverse dimension to the longitudinal dimension) of theimage forming area of the liquid crystal panel 441 is 4:3, the aspectratio of each small lens is also set to be 4:3.

[0078] The second lens array 414 has a substantially similarconfiguration to that of the first lens array 418, and small lenses arearrayed in a matrix therein. The second lens array 414 has a function offocusing the image of each small lens of the first lens array 418 on theliquid crystal panel 441 together with the first condenser lens 416 andthe second condenser lens 419.

[0079] The polarization conversion element 415 is disposed between thesecond lens array 414 and the first condenser lens 416, and unitizedintegrally with the second lens array 414. This polarization conversionelement 415 converts the light from the second lens array 414 into thepolarized light of one kind, and the utilization efficiency of the lightby the electro-optical device 44 can be increased.

[0080] More specifically, each partial light converted in the polarizedlight of one kind by the polarization conversion element 415 issubstantially superposed finally on the liquid crystal panels 441R, 441Gand 441B of the electro-optical device 44 by the first condenser lens416 and the second condenser lens 419. Since only one kind of thepolarized light can be used in the projector 1 using the liquid crystalpanel 441 of the type of converting the polarized light of one kind,substantially one half of the light from the light source lamp 411emitting random polarized light of other kinds is not utilized. Thus, byusing the polarization conversion element 415, the light emitted fromthe light source lamp 411 is completely converted into the polarizedlight of one kind to improve the utilization efficiency of the light inthe electro-optical device 44.

[0081] The color separation optical system 42 comprises two dichroicmirrors 421 and 422, and a reflecting mirror 423, and has a function ofseparating a plurality of sub light beams emitted from the integratorillumination optical system 41 into three color lights of red, green andblue by the dichroic mirrors 421 and 422.

[0082] The relay optical system 43 comprises an incident side lens 431,a relay lens 433, and reflecting mirrors 432 and 434, and has a functionof leading one of the color lights, i.e., blue light separated by thecolor separation optical system 42 to a liquid crystal panel 441B.

[0083] In the dichroic mirror 421 of the color separation optical system42, the blue light component and the green light component of the lightbeam emitted from the integrator illumination optical system 41 aretransmitted therethrough, and the red light component is reflectedthereby. The red light reflected by the dichroic mirror 421 is reflectedby the reflecting mirror 423, and reaches the liquid crystal panel 441Rfor red color through a field lens 417. This field lens 417 convertseach sub light beam emitted from the second lens array 414 into thelight beam parallel to the axis (main beam). The field lens 417 providedon the light incidence side of other liquid crystal panel 441G and 441Bhas a similar function.

[0084] Of the blue light and the green light transmitted through thedichroic mirror 421, the green light is reflected by the dichroic mirror422, and reaches the liquid crystal panel 441G for green through thefield lens 417. On the other hand, the blue light is transmitted throughthe dichroic mirror 422, and passes the relay optical system 43, andreaches the liquid crystal panel 441B for blue light further through thefield lens 417. The relay optical system 43 is used for blue lightbecause the optical path length of blue light is greater than that ofother color lights, and degradation of the utilization efficiency of thelight due to light diffusion or the like can be prevented. This meansthat each of the sub light beams incident on the incidence side lens 431is transmitted through the field lens 417 as it is.

[0085] The electro-optical device 44 has liquid crystal panels 441R,441G and 441B for three light modulators, which comprise, for example,polysilicon TFT used for a switching element, and each color lightseparated by the color separation optical system 42 is modulatedaccording to image information by these three liquid crystal panels441R, 441G and 441B to form an optical image.

[0086] The cross-dichroic prism 45 forms a color image by synthesizingan image modulated for each color light emitted from three liquidcrystal panels 441R, 441G and 441B. The cross-dichroic prism 45 is asubstantially cubic prism formed by affixing four rectangular prisms 451as shown in FIG. 3. A dielectric multi-layer film (not shown) forreflecting the red light having the predetermined wavelength range isprovided on a red color reflective surface 500 comprising a set of twosurfaces 501 and 502 along the extending direction on these interfaces.A dielectric multi-layer film for reflecting the blue light having thewavelength range different from the wavelength range above is providedon a blue color reflective surface 510 comprising a set of two otherreflective surfaces 511 and 512 along the extending direction. Thus,four reflective surfaces 501, 502, 511 and 512 are disposed inside thecross-dichroic prism 45 in an X-shape at right angles. The intersection520 of reflective surfaces 500 and 510 is a line showing the centerposition at the cross-dichroic prism 45. The color image synthesized bythe cross-dichroic prism 45 is emitted from the projection lens 46, andprojected onto a screen in an enlarged manner.

[0087] Other than the cross-dichroic prism 45 of the present embodiment,a cross-dichroic prism in which a red color reflective surface 500 and ablue color reflective surface 510 are located opposite to each other canbe employed. However, description will be made on the abovecross-dichroic prism 45.

[0088] The optical systems 41-45 described above are accommodated withina synthetic resin light guide 47 as shown in FIG. 2. The light guide 47comprises a lower light guide 471 having grooves with optical parts414-419, 421-423 and 431-434 slidably fitted thereinto from the top, anda lid-like upper light guide (not shown) for closing an upper openingside of the lower light guide 471.

[0089] A head part 49 is formed on the light emission side of the lightguide 47. The projection lens 46 is fixed to the front side of the headpart 49, and the cross-dichroic prism 45 with the liquid crystal panels441R, 441G and 441B fitted thereto is fixed.

[0090] [3. Structure of Optical Parts]

[0091] Description will be made below on the structure of the opticalparts with reference to FIGS. 4-6.

[0092] The optical parts include the cross-dichroic prism 45 and theliquid crystal panels 441R, 441G and 441B integrated with each other.

[0093] As shown in FIG. 4, the liquid crystal panels 441R, 441G and 441Bare accommodated in a holding frame 443, and adhered to the light beamincident surface side forming the side surface of the cross-dichroicprism 45 via a metal fixing plate 446 by inserting a transparent resinpin 445 in a hole 443A formed in four corner parts in this holding frame443 together with ultraviolet ray curing adhesive (that is, the fixingto the cross-dichroic prism 45 by a POP (Panel On Prism) structure).

[0094] A rectangular aperture 443B is formed in the holding frame 443,the liquid crystal panels 441R, 441G and 441B are exposed from thisaperture 443B, and this part forms an image forming area. This meansthat the color lights R, G and B are introduced in this part of each ofthe liquid crystal panels 441R, 441G and 441B, and an optical image isformed according to image information. The optical parts comprising theliquid crystal panels 441R, 441G and 441B and the cross-dichroic prism45 integrated with each other is fixed to the lower light guide 471 viaa fixed plate 447 adhered to an upper surface 45A (a surface orthogonalto the light beam incident surface) of the cross-dichroic prism 45.

[0095] The fixed plate 447 has four arm parts 447A extending in fourdirections in plan view as shown in FIG. 4. Of the round holes 447B madein each arm part 447A, two round holes 447B substantially on thediagonal are fitted into positioning projections 474 provided oncorresponding fitting parts, and screws screwed to corresponding fittingparts 473 are in the remaining two round holes 447B. The fixed plate 447has a bulbous swollen part 447C in a center part as shown in FIG. 5. Inaddition, substantially X-shaped reference lines 447D intersected withother on a top part 447C1 of the swollen part 447C are formed on a lowerside of the fixed plate 447. The prism unit 50 is constituted byadhering and fixing the cross-dichroic prism 45 to the fixed plate 447.

[0096] Description will be made on a manufacturing method of the prismunit 50 with reference to schematic diagrams in FIGS. 5 and 6. Since thecross-dichroic prism 45 and the fixed plate 447 are adhered and fixed toeach other in an upside-down manner, FIG. 6 shows the cross-dichroicprism 45 and the fixed plate 447 in an upside-down manner.

[0097] Firstly, while observing the components from the top, the uppersurface 45A (the lower side in FIG. 6) of the cross-dichroic prism 45 isabutted on the top part 447C1 of the swollen part 447C of the fixedplate 447 so that the intersections 520 of four reflective surfaces 501,502, 511 and 512 inside overlap. Then, non-cured ultraviolet ray curingtype adhesive is filled between the cross-dichroic prism 45 and thefixed plate 447. Next, the four reflective surfaces 501, 502, 511 and512 are positioned to the reference lines 447D of the fixed plate 447,and then, the attitude is adjusted to a condition in which the fixedplate 447 is substantially parallel to the upper surface 45A of thecross-dichroic prism 45, in other word, the cross-dichroic prism 45 isnot inclined with respect to the fixed plate 447. After the position ofthe cross-dichroic prism 45 is adjusted with respect to the fixed plate447, the ultraviolet ray is irradiated from the lower surface (the uppersurface in FIG. 6) of the cross-dichroic prism 45 to the upper surface45A to cure the ultraviolet ray curing adhesive.

[0098] [4. Structure of Optical Element Inspection Device]

[0099]FIG. 7 is a front view showing a prism inspection unit 600 for theoptical element inspection device, and FIGS. 8 and 9 are a plan view anda right side view thereof, respectively.

[0100] The prism inspection unit 600 is a device for inspecting therelative position between four reflective surfaces 501, 502, 511 and 512of the cross-dichroic prism 45, and inspecting the manufacturingaccuracy of the prism unit 50 as shown in FIG. 7, and comprises aninspection table 601 with a caster 601A installed on the lower side in amovable manner, and an inspection unit body 602 installed on thisinspection table 601.

[0101] The inspection unit body 602 comprises a pedestal 610 forinstalling the prism unit 50 including the cross-dichroic prism 45 to beinspected via a predetermined holder 611, and an autocollimator 620disposed facing an emission end face 45E of the cross-dichroic prism 45installed on this pedestal 610. The inspection unit body 602 furthercomprises a switching device 630 for a measurement light switching unitdisposed between the autocollimator 620 and the cross-dichroic prism 45,two reflection units 640 and 650 disposed facing incidence end faces 45Band 45R of the cross-dichroic prism 45, a front-to-back measurement CCDcamera 660 disposed on a back side of the reflection unit 650, aright-to-left measurement CCD camera 670 disposed facing the incidenceend face 45G of the cross-dichroic prism 45, a computer 680 whichprocesses the image detected by these two CCD cameras 660 and 670 anddisplays on a monitor 682, and a drive body (not shown) for controllingthe drive of the reflection units 640 and 650.

[0102] In the prism inspection unit 600, the left side, the right side,the proximal side and the distal side viewed from the autocollimator 620described below are set to be the left direction, the right direction,the forward direction, and the rear direction, respectively.

[0103] The pedestal 610 is a member for installing and fixing the prismunit 50 together with other optical parts (not shown) via each holder611 corresponding to the shape, etc. of each optical parts, and thereference lines are formed on the upper surface thereof. Four columns611A are erected on the holder 611 for fixing the prism unit at thepositions corresponding to the round holes 447B of the arm part 447A ofthe fixed plate 447 as shown in FIG. 9. The prism unit 50 is installedand fixed astride upper ends of these four columns 611A.

[0104] The autocollimator 620 introduces the measurement light Xnormally in an emission end face 45E of the cross-dichroic prism 45 asshown in FIG. 10, and detects the return light Y of this introducedmeasurement light X, and is capable of adjusting the position withrespect to the prism unit 50, and comprises an autocollimator body 621and a 3CCD camera 625. This means that the autocollimator 620 integrallycomprises the measurement light introduction unit and the return lightdetection unit of the present invention. In order to normally introducethe measurement light X in the emission end face 45E of thecross-dichroic prism 45, the measurement light X is introduced in fourreflective surfaces 501, 502, 511 and 512 of the cross-dichroic prism 45at the angle of incidence of 45°.

[0105] The autocollimator body 621 comprises a light source unit 622 foremitting the measurement light X, an objective lens 623 for emitting themeasurement light X emitted from the light source unit 622 as parallelbeam, and a light introduction unit 624 for introducing the measurementlight X emitted from the light source unit 622 and the return light Y ofthis measurement light X.

[0106] The light source unit 622 comprises a light source 622A which isdisposed at the back focus position of the objective lens 623, and emitsthe measurement light X which is halogen beam, and a chart 622B with a“+”-shaped transmission aperture formed therein. The measurement light Xemitted from the light source 622A passes through the chart 622B, and isemitted into a light introduction unit 624 as the “+”-shaped measurementlight X.

[0107] The light introduction unit 624 has a half mirror 624A which isdisposed substantially at 45° with respect to the chart 622B of thelight source unit 622, and the measurement light X emitted from thelight source unit 622 is reflected by the half mirror 624A, and formedinto parallel light beam by the objective lens 623.

[0108] The 3CCD camera 625 detects the “+”-shaped return light Y asshown in FIG. 11, and comprises a color separation dichroic prism 626 asa color separation optical system, red color image pickup (R-CCD) 627R,green color image pickup (G-CCD) 627G, and blue color image pickup(B-CCD) 627B disposed on light emitting end faces 626R, 626G and 626B ofthis color separation dichroic prism 626, respectively, and a processingunit 628 included in a computer separate from the computer 680.

[0109] The color separation dichroic prism 626 is formed by affixingthree prisms of predetermined shape, and the “+”-shaped return light Yis separated into three color lights of red light R, green light G, andblue light B.

[0110] Each of image pickup elements 627R, 627G and 627B is electricallyconnected to a processing unit 628, and the image signal detected byeach of the image pickup elements 627R, 627G and 627B is output to theprocessing unit 628.

[0111] The processing unit 628 comprises, as shown in FIG. 12, a videocapture board 628A as an image take-in unit for taking in the imagesignal detected by each of the image pickup elements 627R, 627G and627B, an image processing unit 628B for processing the image signaltaken in by this video capture board 628A, and a reflective surfaceangle difference measurement unit 628C for measuring the angle formed bytwo reflective surfaces 501 and 502 at the red color reflective surface500 and the angle formed by two reflective surfaces 511 and 512 at theblue color reflective surface 510 based on the processed image signal.The details will be described below.

[0112] The return light Y may be visually detected via an eyepiece bydisposing the eyepiece for enlarging the return light Y in place of the3CCD camera 625 though the configuration thereof is not shown in thefigure.

[0113] The switching device 630 introduces the measurement light X onlyinto one of a left side area LA and a right side area RA which are twoareas demarcated by the intersection 520 of the cross-dichroic prism 45when viewed from the introducing direction of the measurement light Xemitted from the autocollimator 620 with reference to FIG. 3, in otherwords, it does not introduce the measurement light X only into eitherthe area LA or the area RA. The switching device 630 is installed on afront side of the pedestal 610 as shown in FIGS. 13 and 14, and comparesa metal, rectangular light shielding plate 631 for shielding themeasurement light X, a sliding part 632 which is fixed to the lower sideof this light shielding plate 631 and slidable in the right-to-leftdirection with respect to the pedestal 610, and an operation part 633fixed to a front side of this sliding part 632.

[0114] As shown in FIG. 13, the sliding part 632 comprises a rail 632Ainstalled on a front surface of the pedestal 610 and extending in theright-to-left direction, and a sliding part body 632B which is fixed tothe lower side of the light shielding plate 631 and slidably provided onthe rail 632A, and the sliding part body 632B is slidable in theright-to-left direction along the rail 632A. The sliding part 632 isdesigned so that the light shielding plate 631 covers only either theleft side area LA or the right side area RA of the cross-dichroic prism45.

[0115] The operation part 633 comprises a long operation part body 633Awhich is screwed to the front side of the sliding part body 632B, ahandle 633B fixed to an upper end part of this operation part body 633A,and a shaft member 633C fixed to a lower end part of the operation partbody 633A and the front side of the pedestal 610, and the handle 633B isturnable around a shaft member 633C thereby.

[0116] Thus, the sliding part body 632B is slidable in the right-to-leftdirection along the rail 632A according to the turn of the handle 633B,and the light shielding plate 631 fixed to the sliding part body 632B isalso moved in the right-to-left direction, and as a result, only eitherthe left side area LA or the right side area RA of the cross-dichroicprism 45 can be covered by the operation of the handle 633B.

[0117] A reflection unit 640 reflects the measurement light X which isintroduced from the autocollimator 620 into the cross-dichroic prism 45,and reflected by the red color reflective surface 500, and returns it tothe autocollimator 620 as the return light Y. As shown in FIG. 9, thereflection unit 640 comprises a rectangular reflecting mirror 641disposed facing the incident end face 45R of the cross-dichroic prism45, and a two-axis adjusting unit 643 which adjusts the position of therotational direction in the horizontal plane and the inclinationdirection of the vertical plane of the reflecting mirror 641 via asupporting plate 642 for supporting this reflecting mirror 641 bycontrolling the drive of a motor, etc. of the drive body.

[0118] A reflection unit 650 reflects the measurement light X which isintroduced from the autocollimator 620 into the cross-dichroic prism 45and reflected by the blue color reflective surface 510, and returns itto the autocollimator 620 as the return light Y. As shown in FIG. 9, thereflection unit 650 comprises a reflecting mirror 651 disposed facingthe incidence end face 45B of the cross-dichroic prism 45, a supportingplate 652 which supports this reflecting mirror 651 on the right sideand has an aperture 652A (FIG. 8) formed at the position correspondingto the intersection 520 of the cross-dichroic prism 45, and a two-axisadjusting unit 653 for adjusting the position of the rotationaldirection of the horizontal plane and the inclination direction of thevertical plane of the reflecting mirror 651 by controlling the drive ofa motor, etc. of the drive body to adjust the three-dimensional positionof this supporting plate 652. The reflecting mirrors 641 and 651 areidentical to each other, and the two-axis adjusting units 643 and 653are also identical to each other.

[0119] A front-to-back measurement CCD camera 660 detects theintersection 520 of the cross-dichroic prism 45 from the right side (theback side) of the reflection unit 650, and is electrically connected tothe computer 680. As shown in FIGS. 8 and 9, this front-to-backmeasurement CCD camera 660 comprises a CCD camera body 661 as anintersection image pickup unit for picking up the image of theintersection 520, and a predetermined micrometer 662 which is movable inboth the longitudinal direction and the right-to-left direction.

[0120] A right-to-left measurement CCD camera 670 detects theintersection 520 of the cross-dichroic prism 45 from the back side ofthe cross-dichroic prism 45, and has the same configuration as that ofthe front-to-back measurement CCD camera 660. The right-to-leftmeasurement CCD camera 670 is capable of moving the CCD camera body 661in both the right-to-left direction and the longitudinal direction bythe predetermined micrometer 662.

[0121] Thus, by adjusting the position of the CCD cameras 660 and 670 inthe longitudinal direction and in the right-to-left direction by themicrometer 662, the focus can be adjusted, and the reference can bepositioned in the intersection image picked up by the CCD cameras 660and 670.

[0122] The computer 680 processes the intersection image of thecross-dichroic prism 45 detected by the two CCD cameras 660 and 670, anddetermines the joining condition of the four reflective surfaces 501,502, 511 and 512, and as shown in FIG. 8, comprises a body 681 having aCPU for executing various programs, a storage device, etc., and amonitor 682 for displaying the determined result.

[0123] As shown in FIG. 15, the body 681 comprises a video capture board681A for converting the image of the intersection 520 respectivelydetected by the two CCD cameras 660 and 670 into the image signal forcomputer, an image processing unit 681B for processing this convertedimage signal, an intersection calculation unit 681C for calculating thewidth and the [angle on] inclination from the reference axis of theprocessed intersection image, a joining condition determining unit 681Dfor determining acceptance or rejection based on the calculated result,and a display unit 681E for displaying the intersection image processedrespectively by the CCD cameras 660 and 670 and the result ofdetermination on the monitor 682, respectively.

[0124] In the above prism inspection unit 600, if the measurement lightX is emitted from the autocollimator 620, this measurement light X isnot introduced in one of the areas LA and RA by the light shieldingplate 631 in the four reflective surfaces 501, 502, 511 and 512 of thecross-dichroic prism 45, while the measurement light X is introducedonly in the remaining area LA or RA. This introduced measurement light Xis reflected by the reflective surfaces 501, 502, 511 and 512, and then,reflected by the reflecting mirrors 641 and 651 to form the return lightY. This return light Y is incident on the cross-dichroic prism 45 again,and reflected by the same reflective surfaces 501, 502, 511 and 512 asthe above, and then, introduced in the autocollimator 620. This returnlight Y is detected by the 3CCD camera 625 in the autocollimator 620.

[0125] [5. Optical Element Inspection Method]

[0126] In this prism inspection unit 600, the inspection of thecross-dichroic prism 45 which is an object for inspection is carried outbased on the flowchart shown in FIG. 16.

[0127] (1) Firstly, before inspecting the cross-dichroic prism 45, theposition of the autocollimator 620 is fixed (Step S1). Morespecifically, the position is fixed based on the flowchart shown in FIG.17.

[0128] (1-1) A substantially regular hexahedron reference mirror block(not shown) with one surface as a mirror surface is disposed at thepredetermined position of the pedestal 610 via a corresponding holder611 so that the mirror surface faces the autocollimator 620 (Step S11).

[0129] (1-2) The measurement light X is emitted from the autocollimator620, and the return light Y which is reflected by the mirror surface isdetected by the 3CCD camera 625 (Step S12).

[0130] (1-3) The position of the measurement light X is fixed byadjusting the autocollimator 620 so that the “+”-shaped image for eachcolor light of the return light Y agrees with the reference position foreach color light indicating the position of the measurement light Xwhile checking the result of detection by the 3CCD camera 625 (StepS13).

[0131] (2) Next, the positions of the reflecting mirrors 641 and 651 ina reflector are fixed (Step S2). More specifically, the positions arefixed based on the flowchart in FIG. 18.

[0132] (2-1) Firstly, a dummy triangular prism (not shown) that issubstantially right-angled prism with an inclined surface of a mirrorsurface is disposed on the predetermined position of the pedestal 610via a corresponding holder 611 so that the mirror surface is at theposition of the red color reflective surface 500, i.e., the mirrorsurface faces the autocollimator 620 and the reflecting mirror 641 (StepS21).

[0133] (2-2) The measurement light X is emitted from the autocollimator620, and the return light Y reflected by the mirror surface, reflectedby the reflecting mirror 641, and reflected by the mirror surface againis detected by the 3CCD camera 625 (Step S22).

[0134] (2-3) After the position of the reflecting mirror 641 is adjustedby the two-axis adjusting unit 643 so that the “+”-shaped image of thereturn light Y for each color light agrees with the reference positionfor each color light indicating the position of the measurement light Xwhile checking the result of detection by the 3CCD camera 625, and thereflecting mirror 641 is fixed (Step S23).

[0135] (2-4) Then, the dummy triangular prism (not shown) that is asubstantially right-angled prism is rearranged to be at thepredetermined position of the pedestal 610 via the same holder 611 sothat the mirror surface is at the position of the blue color reflectivesurface 510, and in the similar procedure as the above, the position ofthe reflecting mirror 651 is adjusted by the two-axis adjusting unit653, and then, the reflecting mirror 651 is fixed (Step S24).

[0136] (3) Next, the positions of the two CCD cameras 660 and 670 arefixed (Step S3). More specifically, the positions are fixed based on theflowchart shown in FIG. 19.

[0137] (3-1) Firstly, as shown in FIG. 20, substantially rectangularparallelopiped block 701 made of metal or glass for detecting edge, anda rectangular parallelopiped dummy glass 702 of one half thickness ofthe cross-dichroic prism 45 are prepared. Next, the block 701 isdisposed at the predetermined position of the pedestal 610 via thecorresponding holder 611 so that an apex 701A of this block 701 is atthe center position C of the holder 611, and a ridge 701B of the block701 is at the center position C of the holder 611. In addition, a dummyglass 702 for preventing focus shift caused by the difference betweenthe index of refraction in glass and the index of refraction in air isdisposed normal to the optical axis of the front-to-back measurement CCDcamera 660 between the block 701 and the front-to-back measurement CCDcamera 660 (Step S31).

[0138] (3-2) In this condition, the image of the ridge 701B of the block701 is picked up by the front-to-back measurement CCD camera 660, andthe focus of the taken-in image is adjusted by advancing or retractingthe front-to-back measurement CCD camera 660 in the direction of thedummy glass 702 (the vertical direction in the figure). Then, theposition of the front-to-back measurement CCD camera 660 is adjusted inthe right-to-left direction in the figure so that the image of the ridge701B of the block 701 agrees with the reference position indicating thecenter position C (Step S32).

[0139] (3-3) Next, the block 701 is left as it is, and the dummy glass702 is repositioned so that it is normal to the optical axis of theright-to-left measurement CCD camera 670 between the block 701 and theright-to-left measurement CCD camera 670 (Step S33).

[0140] (3-4) In this condition, the image of the ridge 701B of the block701 is picked up by the right-to-left measurement CCD camera 670, andthe focus of the taken-in image is adjusted by advancing or retractingthe right-to-left measurement CCD camera 670 in the direction of thedummy glass 702 (the right-to-left direction in the figure). Then, theposition of the right-to-left measurement CCD camera 670 is adjusted inthe vertical direction in the figure so that the image of the ridge 701Bof the block 701 agrees with the reference position indicating thecenter position C (Step S34). Thus, the positions of the two CCD cameras660 and 670 are adjusted and fixed.

[0141] (4) Next, the prism unit 50 to be inspected is correctlyinstalled and fixed at the predetermined position of the pedestal 610via the corresponding holder 611 (Step S4).

[0142] (5) Now the preliminary preparation of the inspection iscompleted, and in this condition, the directions of the blue colorreflective surface 510 and the red color reflective surface 500 withrespect to fixed plate 447 are inspected in the cross-dichroic prism 45of the prism unit 50 (Step S5). More specifically, the directions areinspected based on the flowchart in FIG. 21.

[0143] (5-1) The measurement light X emitted from the autocollimator 620into the end face 45E of the cross-dichroic prism 45 with the lightshielding plate 631 inserted therein, is reflected by the bluereflective surface 500 to form the blue measurement light XB, and then,reflected by the reflecting mirror 651 to form the return light YB, andthe return light YB reflected by the blue reflective surface 500 againis returned to the autocollimator 620. Then, the position of this returnlight YB is detected by the image pickup element 627B of the 3CCD camera625, this detection signal is taken in by the video capture board 628A,and this detection signal is image-processed by the image processingunit 628B. This processed image is displayed on the display D (FIG. 22),and stored in a memory or the like in the computer (Step S51).

[0144] (5-2) Next, based on the deviation D1 in the vertical directionon the display D shown in FIG. 22 between the preset reference positionand the position of the processed image, the rotational deviation θB1 ofthe blue color reflective surface 510 with respect to the referenceposition is calculated as shown in FIG. 23 (Processing S52).

[0145] (5-3) Further, based on the deviation D2 in the right-to-leftdirection shown in FIG. 22, the inclination θB2 with respect to thereference position, i.e., the tilt quantity with respect to the axis ofillumination light is calculated as shown in FIG. 24 (Step S53).

[0146] (5-4) Similarly, the red return light YR which is emitted fromthe autocollimator 620 and reflected by the red color reflective surface500 and the reflecting mirror 641 is detected by the 3CCD camera 625,and the rotational deviation θR1 and the inclination θR2 shown in FIGS.23 and 24 are calculated (Processing S54). The acceptable ranges forboth the rotational deviation θB1 and θB2, and the inclination θR1 andθR2 are ±5 minutes, respectively.

[0147] (6) Next, the light shielding plate 631 is set, and the relativepositions between the reflective surfaces 501, 502, 511 and 512 at thecross-dichroic prism 45 of the prism unit 50 are inspected (Step S6).More specifically, the relative positions are inspected based on theflowchart in FIG. 25.

[0148] (6-1) The measurement light X is emitted from the autocollimator620 to the right side area RA, and the return light Y reflected by thereflecting mirrors 641 and 651 is detected by the 3CCD camera 625 (StepS61: measurement light introducing procedure and return light detectingprocedure). More specifically, the blue light XB out of the measurementlight X is reflected by the blue color reflective surface 510, and then,reflected by the reflecting mirror 651 to form the blue return light YB,and again reflected by the blue color reflective surface 510, andreturned to the autocollimator 620. Then, the position of this bluereturn light YB is detected by the image pickup element 627B of the 3CCDcamera 625, the detected signal is taken in by the video capture board628A, and this detected signal is image-processed by the imageprocessing unit 628B. This processed image is displayed on the displayD, and stored in a memory or the like in the computer.

[0149] (6-2) Next, the measurement light X is emitted to the left sidearea LA by operating the handle 633B of the switching device 630 in asimilar manner to Step S61, and the blue return light YB reflected bythe reflecting mirror 651 is detected by the 3CCD camera 625 (Step S62:measurement light switching procedure).

[0150] (6-3) FIG. 26 shows the result of detection of the case in whichthe blue color reflective surface 510 (512) of the right side area RA isdeviated from the blue color reflective surface 510 (511) of the leftside area LA. The reflective surface angle difference measuring unit628C. The reflective surface angle difference measuring unit 628Ccalculates the horizontal deviation PB of the blue color reflectivesurface 510 (511) of the left side area LA with reference to the bluecolor reflective surface 510 (512) of the right side area RA, i.e., thedeviation (the angle formed) from the extending directions of thereflective surfaces 511 and 512 as shown in FIG. 27 based on thedeviation DB1 in the vertical direction (Step S63: deviation detectingprocedure). The acceptable range of this horizontal deviation PB is ±15seconds.

[0151] (6-4) Next, the vertical deviation QB (not shown) which is theangle formed by the blue color reflective surface 510 (511) of the leftside area LA with reference to the blue color reflective surface 510(512) of the right side area RA based on the deviation DB2 in theright-to-left direction shown in FIG. 26 (Step S64: deviation detectingprocedure). The acceptable range of this vertical deviation QB is also±15 seconds.

[0152] (6-5) Similar to the case of the blue light, by operating theswitching device 630 (Processing S65), the reflective surface angledifference measuring unit 628C calculates the horizontal deviation PRand the vertical deviation QR (not shown) between the red reflectivesurfaces 501 and 502 shown in FIG. 27 based on the deviations DR1 andDR2 with reference to the red color reflective surface 500 (502) of theright side area RA (Processing S66).

[0153] (7) Next, the joining condition (the joining and fixing accuracy)of the fixed plate 447 to the cross-dichroic prism 45 of the prism unit50 is inspected (Step S7). More specifically, the joining condition isinspected based on the flowchart in FIG. 28.

[0154] (7-1) In the preliminarily fixed front-to-back measurement CCDcamera 660, the CCD camera body 661 picks up the image of theintersection 520, and based on the image picked-up and image-processedintersection 520, the intersection calculation unit 681C calculates thedeviation T1 in the longitudinal direction of the intersection 520 withrespect to the reference line, the width dimension T2 of theintersection 520 with respect to the reference line, and the inclinationφ with respect to the reference line as shown in FIG. 29 (Step S71: theintersection image acquiring procedure). The width dimension T2 of theintersection 520 is measured, and if the width dimension T2 of theintersection 520 is larger than the reference value, it can be confirmedthat a translating deviation is generated between the extending fourreflective surfaces 501, 502, 511 and 512.

[0155] The acceptable range of the deviation T1 in the longitudinaldirection is ±0.05 mm. In addition, the acceptable ranges of the widthdimension T2 and the inclination φ are also appropriately set.

[0156] (7-2) Similarly to the above, in the right-to-left measurementCCD camera 670, the deviation T1 in the right-to-left direction of theintersection 520 with respect to the reference line, the width dimensionT2 of the intersection 520, and the inclination φ with respect to thereference line are calculated by picking up the image of theintersection 520 by the CCD camera body 671 (the intersection imageacquiring procedure) (Step S72).

[0157] (8) When the above operations are completed, the joiningcondition determining unit 681D determines whether the measureddeviations T1, T2 and φ are all in acceptable ranges (Step S8: joiningcondition determining procedure). If the measured deviations are withinthe acceptable range, the prism unit is determined to be an acceptableone, and if the measured deviations is outside the acceptable range, theother prism unit is determined to be a rejected one. The acceptance orrejection of other deviations may also be determined automatically.

[0158] (9) Finally, all the inspections are completed by detaching theprism unit 50 from the predetermined holder 611 (Step S9).

[0159] [6. Advantages]

[0160] The following advantages can be obtained according to thisembodiment.

[0161] (1) Since the measurement light X is emitted from theautocollimator 620 and this measurement light X is switched forinspection so that it is directed to the right side area RA or the leftside area LA of the color reflective surfaces 500 and 510 by theswitching device 630, the relative positions of the four reflectivesurfaces 501, 502, 511 and 512 of the color reflective surfaces 500 and510 can be easily inspected. Thus, the acceptance or rejectiondetermination accuracy of the cross-dichroic prism 45 can be heightened.In addition, the cross-dichroic prism 45 which is determined to beacceptable in these inspections is included in the projector 1, theprojected image by the projector 1 can also be sharpened.

[0162] (2) By employing the autocollimator 620 with the measurementintroduction unit and the return light detection unit integrated witheach other, the inspection device 600 can be miniaturized compared witha case in which the measurement introduction unit and the return lightdetection unit are separately disposed from each other.

[0163] (3) By installing the reflecting mirrors 641 and 651 on the endfaces 45R and 45B of the cross-dichroic prism 45, the bright returnlight Y can be reliably introduced, and easily detected by theautocollimator 620.

[0164] (4) By employing the 3CCD camera 625 for detecting the returnlight Y, the return light Y can be more reliably and automaticallydetected compared with a case in which the return light is detected, forexample, visually, and the burden on an operator can be reduced.Alternatively, a configuration is also possible, in which a plurality ofcolor filters consisting of each color are provided, the return light Yis successively passed through these color filters, and the return lightY is detected by the return light detection unit for each color light.However, the return light Y can be detected more easily than a case inwhich the 3CCD camera 625 is employed, since the color filters need notbe replaced.

[0165] (5) The return light Y is detected by the image pickup elements627R, 627G and 627B, this detected signal is taken in by the videocapture board 628A, the taken-in image signal is image-processed by theimage processing unit 628B, and the reflective surface angle differencemeasuring unit 628C calculates the angle formed between the fourreflective surfaces 501, 502, 511 and 512 of the color reflectivesurfaces 500 and 510. Thus, by setting the acceptable range of the angledeviations PR and PB in advance, the angle deviations PR and PB betweenthe four reflective surfaces 501, 502, 511 and 512 of the colorreflective surfaces 500 and 510 can be easily and automaticallyinspected.

[0166] (6) The width dimension T2 of the intersection 520 is measured bythe CCD cameras 660 and 670, and the deviation of this translation canbe easily inspected even when the four reflective surfaces 501, 502, 511and 512 of the color reflective surfaces 500 and 510 are translated anddeviated. The inclination φ of the intersection 520 is measured by theCCD cameras 660 and 670, and this inclination φ can be easily inspectedeven when the four reflective surfaces 501, 502, 511 and 512 of thecolor reflective surfaces 500 and 510 are inclined and deviated from thereference axis normal to the optical axis of the measurement light X.Similarly, the deviation T1 in the longitudinal and right-to-leftdirections can be easily inspected. Since the acceptable ranges of thedeviation T1, the width dimension T2 and the inclination φ are set inadvance, they can be easily and automatically inspected.

[0167] (7) Since the switching device 630 has a relatively simplestructure that makes it possible to switch the light shielding plate 631by simply operating the handle 633B, the cost of the switching device630 can be suppressed.

[0168] [7. Modification]

[0169] The present invention is not limited to the above embodiment, butincludes other configurations capable of achieving the object of thepresent invention, and modifications shown below are also included inthe present invention.

[0170] For example, in the above embodiment, the reflection units 640and 650 are disposed facing the end faces 45R and 45B of thecross-dichroic prism 45, but the present invention is not limitedthereto. For example, a reflecting mirror may be affixed to the endfaces 45R and 45B of the cross-dichroic prism 45. However, the aboveembodiment has an advantage in that the position of the reflectingmirror can be adjusted correctly. In addition, the light may bereflected by each end face without providing any reflecting mirror orthe like.

[0171] In the above embodiment, the cross-dichroic prism 45 of the colorsynthesis optical system is inspected as the optical element, but thepresent invention is not limited thereto. A color separation opticalsystem or the like including affixed mirrors may be inspected. Further,in the above embodiment, the inspection order of the inspection items isnot limited to the above order.

[0172] In the above embodiment, the CCD cameras 660 and 670 are manuallyadjusted, but may be automatically adjusted. In addition, theautocollimator 620 may be automatically adjusted.

[0173] Furthermore, the switching device may be configured so that itincludes a groove, for exmaple, into which an end of the light shieldingplate can be inserted, thereby making it possible to perform switchingof the light shielding areas by placing the light shielding plate intoor out of the switching device along this groove. In this case, theconfiguration is relatively simple, and the cost of the switching devicecan be suppressed. A material of the light shielding plate is notlimited to metal, but any other materials such as resin may beacceptable if they have light shielding function. In this condition, theshape of the light shielding plate is not limited either.

[0174] In addition, in the switching device 630 of the above embodiment,the handle 633B is manually operated, and may be automatically switched.

[0175] In the above embodiment, the 3CCD camera 625 is employed in theautocollimator 620, but the present invention is not limited to.Detection may be performed by a regular CCD camera or visually.

[0176] In the above embodiment, the autocollimator 620 is employed, andthe measurement light introduction unit and the return light detectionunit are integrated with each other. However, the measurement lightintroduction unit and the return light detection unit may be separatefrom each other.

[0177] In the above embodiment, the acceptable range of thecross-dichroic prism 45 is not limited to the above numerical values.This means that the acceptable range may be changed appropriatelyaccording to the model and the purpose of the optical appliances such asthe projector to be built therein.

[0178] [Advantage of the Invention]

[0179] As described above, the optical element inspection device and theoptical element inspection method according to the present inventionhave an advantage that the relative position of each reflective surfacecan be inspected.

What is claimed is:
 1. An optical element inspection device forinspecting the relative positions of each reflective surface of anoptical element having four reflective surfaces disposed in an X-shapeso as to form an angle of incidence of 45° when viewed from a directionorthogonal to an optical axis of an incident light beam so that one setof reflective surfaces along one extending direction of the X-shapereflect the light beam of a wavelength range different from that of theother set of reflective surfaces, comprising: a pedestal on which theoptical element to be inspected is installed; a measurement lightintroduction unit for introducing measurement light at the angle ofincidence of 45° with respect to any of said four reflective surfaces; areturn light detection unit for detecting return light of themeasurement light introduced in said optical element from themeasurement light introduction unit; and a measurement light switchingunit for introducing said measurement light only in either area of twoareas demarcated by the intersection of one set of the reflectivesurfaces with the other set of the reflective surfaces when viewed fromthe introducing direction of said measurement light.
 2. An opticalelement inspection device according to claim 1, wherein said measurementlight introduction unit and said return light detection unit areintegrated with each other to form an autocollimator.
 3. An opticalelement inspection device according to claim 1 or claim 2, furthercomprising: a reflecting member which reflects light beam reflected bysaid reflective surface and introduces the light beam in said returnlight detection unit as return light.
 4. An optical element inspectiondevice according to any one of claims 1 to 3, wherein said return lightdetection unit includes a color separation optical system for separatingreturn light into a plurality of color lights, and a plurality of imagepickup elements each corresponding to each color light separated by saidcolor separation optical system.
 5. An optical element inspection deviceaccording to claim 4, further comprising: an image take-in unit fortaking in a signal detected by said image pickup element; and areflective surface angle difference measurement unit which performsimage processing of the image signal taken in by said image take-inunit, and measures an angle formed by said one set of reflectivesurfaces or said other set of reflective surfaces.
 6. An optical elementinspection device according to any one of claims 1 to 5, furthercomprising: an intersection image pickup unit for picking up an image ofthe intersection of said one set of reflective surfaces with said otherset of reflective surfaces; and a joining condition determination unitfor determining the joining condition of each reflective surface from awidth and an inclination of said intersection based on the signaldetected by said intersection image pickup unit.
 7. An optical elementinspection method for inspecting the relative positions of eachreflective surface of an optical element having four reflective surfacesdisposed in an X-shape so as to form an angle of incidence of 45° whenviewed from a direction orthogonal to an optical axis of an incidentlight beam so that one set of the reflective surfaces along oneextending direction of the X-shape reflect light beam of a wavelengthrange different from that of the other set of reflective surfaces,comprising: a measurement light introducing procedure of introducing themeasurement light at the angle of incidence of 45° in any of thereflective surfaces of the optical element to be inspected; a returnlight detecting procedure of detecting return light of the measurementlight introduced into said optical element by said measurement lightintroducing procedure; a measurement light switching procedure ofswitching the measurement light so that it is introduced into anotherreflective surface along said any of the reflective surfaces; and adeviation detecting procedure of detecting the return light of theswitched measurement light, and detecting the deviation of the otherreflective surface with respect to said any of the reflective surfaces.8. An optical element inspection method according to claim 7, furthercomprising: an intersection image acquiring procedure of acquiring animage of the intersection of said one set of reflective surfaces withsaid other set of reflective surfaces; and a joining conditiondetermining procedure of determining the joining condition of eachreflective surface from the width and the inclination of saidintersection.